1. Field of the Invention
The invention relates to a display device, in particular in a motor vehicle, having a display that can be illuminated by a light source, and a light guide arranged between the light source and display, the light source having several individual light sources whose overall light-emitting surface is larger than the surface of the display.
2. Description of the Prior Art
Such display devices are known, and are used, for example in motor vehicles for instrument illumination. By contrast with displays that can be illuminated by intense individual light sources such as, for example, halogen lamps or fluorescent lamps, these devices can have a lower power consumption and reduced heat loss emission.
For reasons of traffic safety, there is an urgent need in motor vehicles for the individual display instruments to have a brightness that enables them to be read even given high ambient brightness. This is also of great importance, in particular, for so-called headup displays where—as described in DE 198 52 842 C1, for example—an image is reflected into a front pane of the motor vehicle. Because of the constricted space conditions generally applying in the region of the dashboard of the motor vehicle in which the display device is fitted, and of the therefore problematic use of intense light sources that, firstly, require a large installation space and, secondly, emit a substantial heat loss, an attempt is being made to replace the individual light source by a plurality of light sources that admittedly each have a low light intensity per se, but which also have a low heat loss emission. The problem arises in this case that because of geometric boundary conditions—the miniaturization of these light sources is limited—the arrangement of light sources requires a larger surface than that to be illuminated.
A known solution to this problem consists in arranging between the light sources and display a light guide in the form of a solid pyramidal frustum whose base surface adjoins the light sources and which tapers in the direction of the display. Owing to this shape of the light guide, the light beams emerge from the light guide at a larger angle than that at which they entered it. This opposes the requirement for a narrow light emission angle that ensures a high intensity of illumination. Again, there are disadvantageous light losses owing to the exit of light at the side surfaces of the light guide, since the light beams impinge on the surface on each reflection at a relatively large angle near the perpendicular, and the total reflection is thereby cancelled.